Crystal resonators, crystal filters, crystal oscillators, and other piezoelectric resonator devices are examples of electronic components requiring hermetic sealing. In all of these products, excitation electrodes are formed on the major surfaces of a crystal resonator element and these excitation electrodes are hermetically sealed by the main body casing of the piezoelectric resonator device in order to protect the excitation electrodes from ambient atmosphere.
In piezoelectric resonator devices, the main body casing is made up of a base and a lid. Such piezoelectric resonator devices include devices, in which the base and lid are directly seam-bonded using a metal ring for seam welding, thereby forming the interior space of the main body casing and simultaneously hermetically sealing the interior space, with a piezoelectric resonator element held inside said interior space (for example, see Patent Document 1).
The main body casing of the piezoelectric resonator device disclosed in Patent Document 1 comprises a ceramic package (referred to as “base” in this Detailed Description) of a concave cross-section containing a crystal resonator element (referred to as “piezoelectric resonator element” in this Detailed Description), and a metal lid bonded to the opening portion of this base (referred to as “lid” in this Detailed Description). The main body casing, which hermetically seals the crystal resonator element, is formed by bonding a metal ring for seam welding with the help of a silver braze material to create a joint portion on the base and then bonding the lid to the base over the metal ring using seam welding (a type of resistance welding).
Moreover, there is a method (e.g. see Patent Document 2) based on a technology that is different from Patent Document 1, in which a metal ring is not used and, instead, upon forming a metal film (e.g. a multi-layer configuration of tungsten-nickel-gold) on a base and forming, for instance, silver solder (copper-silver alloy) on a lid, the metal film portion of the base and the silver solder of the lid are bonded together using a seam welding technique. Because this method utilizes a metal film instead of using a metal ring in order to accomplish direct seam welding (bonding), Patent Document 2 allows for low height geometry to be achieved for the main body casing (base).
Patent Document 1: JP2004-64217A.
Patent Document 2: JP2000-236035A.